PENTAX respond on the K/M exposure problem

[Zvio]

After three failed attempts to get a coherent answer, they finally came up with this "answer"... Let's see what the forum members think of that:

Dear Sir/Madam,

Thank you for your enquiry.

The use of old K-lenses is restricted on d-SLR cameras!
There is no fix because this is related to the construction of those old lenses.

Metering using the green button will only work correct when having the aperture fully open.

These lenses do NOT have the required electronic contacts to transmit the aperture opening to the camera.

I hope that your question has been answered to your satisfaction.

Should you have further questions regarding this matter, please do not hesitate to contact us again.

When replying, please make sure this email is included.

With kind regards,

Wim van Kleef
Pentax Digital Camera Support Team

Your Email:
[Hide Quoted Text]

Your Email:
Dear Sir/Ms,

No, the problem I reported did not go away! Here it is once more:

I own 5 pentax cameras starting from the MX through *istD and now
K10D. My 5 M-lenses that still work perfectly on the *istD do not meter
as they should on the K10D; Specifically, the metering is OK when the
aperture is fully open but when stopping down the metering reading
(upon pressing the green button) causes consistently overexposure on
all 5 lenses.

I am working with the M-mode and, of course, have set the

"A-ring" option to enable shooting with these old lenses...
This problem exists also in many other K10D as reported in the Pentax
Forum on Dpreview. We all urge you to find a solution!! Check out the
Dpreview Forum, and let me know if you need help in that!!!

 

[John Bean (UK)]

That appears to be no answer at all, and is factually incorrect into the bargain. Disappointing response.

--
John Bean [GMT - is there any other?]

PAW 2007 Week 5:
http://waterfoot.smugmug.com/gallery/2321711/1/127460306/Large



Index page: http://waterfoot.smugmug.com
Latest walkabout (4 April 2006): http://waterfoot.smugmug.com/gallery/1348582

 

[LuzArt]

Good to see the left hand knows what the right hand is doing...

Ben
--

 

[flash1100]

Disappointing response. As John states it is factually incorrect. I think they might be trying to make you go away. Has anyone emailed the US Pentax service division?

I will email CR Kennedy here in Australia. I emailed them about my AF200T trigger voltage and have received no response. I ended up phoning the service section in Melbourne. Perhaps I can try that again, I still have the chaps name I spoke to - he seemed quite helpfull. Anyone in Melbourne care to try phoning - I live in perth, it tends to get expensive...
--
Cheers

Gordon
Perth, Western Australia

I got the K10D!

http://www.pbase.com/gordonhaywood

 

[blende8]

The so called "Support Team" is an out-sourced Call-Center without qualified personnel. I have tried to ask them something several times. The answers were equally funny always.
Try to contact someone directly from Pentax.

 

[Bich]

The author of the answer is manifestly incompetent. We could have accepted this argument before the first upgrade of the *istD. Now he has to explain why the green button trick works perfectly on the *istD (and the following reflexes before the K10 I suppose) and what has changed.
--
Jacques Bijtebier

 

[Alek79]

Hi Zvio,

Thanks for sharing with us the "reply". I'm not going to comment on that...

Anyway, I've been wondering whether this forum has seen a contribution to this issue from the Pentax employees we all know. I know of at least two forum members who work for Pentax and post here quite regularly. When I started this thread

http://forums.dpreview.com/forums/read.asp?forum=1036&message=21772399 I was hoping to draw the attention of the Pentax staff lurking on the forum. Apparently, no feedback from their part.
Cheers,
Al

 

[arzvael]

--
-

 

[XavierP56]

What do they answer when you tell them it was working in the istDS ?

It's also clearly written in the manual that exposure errors may appear using manual lens.

My guess : Pentax is probably aware of the issues that the new focusing screen is bringing but decided that backward compatibility was less important than a bright focusing screen. That's a perfectly valid point because if the exposure is right wide-open, it is easy to compute it for any aperture...

Call that a feature, not a bug ?

 

[Joseph Tainter]

Obviously an inept answer.

I recall that last fall, when the K10d was imminent, Pentax was telling the world that it would work with 24 million old lenses. I believe Samsung claimed something similar.

Joe

 

[Jos de Bont]

What do they answer when you tell them it was working in the istDS ?

It's also clearly written in the manual that exposure errors may
appear using manual lens.

My guess : Pentax is probably aware of the issues that the new
focusing screen is bringing but decided that backward compatibility
was less important than a bright focusing screen. That's a
perfectly valid point because if the exposure is right wide-open,
it is easy to compute it for any aperture...

If the camera knows what the apperturesetting is, yes. But the camera does not know which apperture is set on the lens and does not know what the apperture is wide open, so it has nothing to calculate. Perhaps this could work if you tell the camera what the apperture is wide-open and/or all closed, in the same way you can tell the camera what the focuspoint of the lens is. In that case you could perhaps set the apperture the lens all closed and set the apperture on the camera in stead on the lens and the camera can compute shuttertime and close the apperture itself. I don't know if this coul be a sollution and it's not the most comfortable sollution, but I could live with it.

Call that a feature, not a bug ?

 

[andr52]

I have got my k10d a few days ago and tested all my old lenses with this camera. Of course I have the same bad exposures related in this forum with the M lenses so I have tried to find the origin of this problem and I have compared the bayonnet from my old Pentax Z20 to the K10d . There is a big difference between them, we can find a small pin on the right side of the Z20 who moves mechanicaly when we turn the diaphragma ring from a M lens (there is also a pin in the lens), I cannot find this in the K10d so I think the K10d doesn’t know wich aperture is setting on the lens, he can only mesure the light coming inside on the full aperture! I use my M lenses only in manual mode mesuring the light in full aperture and compute the speed for the other aperture, it works well but it is not pratical. I’m dissapointing.
I hope this can help.

--
André

 

[corlissnc]

I have absolutely no problem. I have a manual Rikenon 28-100 (w. macro function) that I have successfully used on my istD AND on my new K10D. I've allowed in the camera's settings that F stop settings other than "A" are allowed and I use the lens in "M" mode where the camera (with a press of the green button) sets the appropriate shutter speed. This lens does not (of course) have the pins to let the camera know what aperture is set BUT I do hear the lens stop down TO THE SET F-STOP when the green button is pressed so that METERING is taking place and an APPROPRIATE shuuter speed is being set.

Somebody here in this thread is claiming that you only get proper exposure if the lens is set to its wide open F-stop but that's simply NOT TRUE. I know for a fact it's not true because (with the same scene) I get a different shutter speed as I change the F-stop from F-4 (wide open) to F-5.6 to F-8, F-11, F16 and F-22. And the exposure is always correct with any of these 6 different f-stops (and 6 different shutter speeds). All that's happening here is the same thing the old match needle cameras used to do ---- they didn't know what f-stop was set on the lens --- there were no pins to communicate this to the camera --- the lens was stopped down, the light was measured, the camera knew what film speed was set and you set the shutter speed to match the needles. Same thing is happening with the istD/DS and K10D except that there are no needles and we do not have to rotate a shutter speed dial --- shutter speed is automatically set with the press of the green button.

All it is, is algebra ----- you know X and Y and you can always solve for Z. X is the light the camera measures when the lens is stopped down at the press of the green button (I hear it happening), Y is the ISO the camera is set for and the camera then MUST solve for Z (the shutter speed). And I repeat --- I get six different shutter speeds for the six different F-stops AND a properly exposed photo all six ways so what is this discussion all about??

 

[Zvio]

The problem appears because the metering in M-mode and upon pressing the GB is off whenever most of the light rays hit the focusing screen perpendiculary. Then, not enough light is scattered off the screen to reach the sensor resulting in a wrong estimate of light intensity...This is usually the case with a lens being stopped down below a certain f#...

Now, that severity of the problem dependes on two factors; langle of light incidence and the degree of diffusion affected bt the screen on one hand, and lens design on the other.

So, please try different lenses, different f's etc before barging in with "what the fuss is all about"... some of us have a problem, some others do not, or do not know they do.

 

[mermoz]

Yes I think it would be the best solution and can be implemented as followed:

firmware modifcation for correct mettering in M-mode with K10D and M-lenes:

-when power on the camera, the display shows focal lenght setting AND wide open aperture setting on the same screnn and one can be set with the rear e-dial and the other with the front e-dial.

• while shooting, each time you change the lens aperture ring setting, like you can set the shutter speed whit the front dial, dial-in with the rear e-dial the ring aperture value that is now displayed in the viewfinder instead of F--.

• when you press now the green button the camera meters wide open and calculate the correct shutter speed.

this would solve the K10D M-lens mettering issue without to much annoyance

Call that a feature, not a bug ?

 

[LazySod]

[...] I have compared the bayonnet from my old Pentax
Z20 to the K10d . There is a big difference between them, we can
find a small pin on the right side of the Z20 who moves mechanicaly
when we turn the diaphragma ring from a M lens (there is also a pin
in the lens), I cannot find this in the K10d [...]

You haven't discovered anything new. All Pentax DSLRs, and some of their later AF film SLRs, lack the aperture indexing pin. So with M-type lenses, a DSLR has to stop down the lens when metering. But apparently stop down metering isn't reliable on the K10D (and possibly the K100D/K110D), at least for some camera bodies or some lenses.

 

[XavierP56]

I think the lens design is probably very important. However, metering wide-open and then doing very easy math for the requiered aperture is not a big deal...

 

[Zvio]

You are right but it is time consuming (I mean to meter wide open, not the in-head calculation which I agree is a cinch...). On 90% of the cases I shoot with one and the same f# (the optically optimum which is usually in the range of f8-f16), and I know the fudge-factor that I need to introduce after pressing the GB...then just click-click-click- and shoot! Can't be simpler...

 

[XavierP56]

By the way, have you tried answering Pentax's response ?
If so, what did they answer ?

 

[Bich]

with my K10 the measure wide open is not correct either. The error depends on the ambiant luminosity. My opinion is that the meter itself do not respond correctly to the light when the lens is in non-A position. A table of the correction for each given IL would be useful, if it turns out to be independent on the other parameters (lens, aperture, ISO, etc...): for IL x the correction would always be f(x). But I am afraid the error is partially erratic. In one of my tests the meter was suddenly absolutely correct, but it is no more the case. I think Pentax simply did not care on the behaviour of the meter with lenses in non-A position. The millions of lenses to which the advertisements refer begin perhaps with the KA series.

Question: the K10 handbook is not clear for the green button trick with M lenses. The D handbook says nothing since it was printed before the upgrade. But what about the handbooks of the DS, DL, K100?
--
Jacques Bijtebier